A. Field of the Invention
The present invention relates generally to stable three-phase emulsions that include an external aqueous-gel phase and an internal water-in-oil phase. The emulsions can be used in cosmetic, food, and pharmaceutical applications.
B. Description of Related Art
Emulsions have been used in the cosmetics and pharmaceutical fields. The most prevalent type of emulsions used are two-phase oil-in-water and water-in-oil emulsions. The use of three-phase emulsions has increased in recent times.
However, three-phased emulsions have been shown to have stability problems. For instance, U.S. Pat. No. 6,464,966 explains a frequently encountered stability problem with water-in-oil-in water emulsions, where the internal droplets of water from the water-in-oil primary phase migrate through the oil phase and into the external aqueous phase. This type of migration can result in the coalescence of the internal droplets and release of the same into the aqueous external environment. Ultimately, this migration can lead to phase inversion which results in an unstable two-phase oil-in-water emulsion and a generally unusable product.
U.S. Pat. Nos. 6,464,966 and 6,358,500 attempt to solve the stability problem by introducing partially or completely crosslinked organopolysiloxane elastomers having a polyoxyethylenated or polyoxypropylenated chain into the oil phase of a water-in-oil-water triple emulsion. The use of such elastomers can lead to increased costs in preparing the three-phase emulsion and require large amounts of energy to function properly.
U.S. Pat. Nos. 6,290,943 and 6,235,298 disclose water-in-oil-in-water emulsions. These patents appear to suggest that the stability of their emulsions hinge on the use of an isotropic aqueous outer phase. These patents also explain that the use of surfactants having an HLB value of greater than 10 and the amount of such surfactants within the emulsion can contribute to the instability of multiple phase emulsions.